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Cisco ME 3800X and 3600X Switch Software Configuration Guide
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Chapter 26 Configuring Network Security with ACLs
Understanding ACLs
You configure access lists on a router or Layer 3 switch to provide basic security for your network. If
you do not configure ACLs, all packets passing through the switch could be allowed onto all parts of the
network. You can use ACLs to control which hosts can access different parts of a network or to decide
which types of traffic are forwarded or blocked at router interfaces. For example, you can allow e-mail
traffic to be forwarded but not Telnet traffic. ACLs can be configured to block inbound traffic, outbound
traffic, or both.
An ACL contains an ordered list of access control entries (ACEs). Each ACE specifies permit or deny
and a set of conditions the packet must satisfy in order to match the ACE. The meaning of permit or deny
depends on the context in which the ACL is used.
The switch supports IPv4 ACLs and Ethernet (MAC) ACLs:
•
IP ACLs filter IPv4 traffic, including TCP, User Datagram Protocol (UDP), Internet Group
Management Protocol (IGMP), and Internet Control Message Protocol (ICMP).
•
Ethernet ACLs filter non-IP traffic.
Note
MAC ACLs are not supported on ports configured with service instances.
This switch also supports quality of service (QoS) classification ACLs. For more information, see the
“Understanding QoS” section on page 27-2
.
These sections contain this conceptual information:
•
Supported ACLs, page 26-2
•
Handling Fragmented and Unfragmented Traffic, page 26-5
Supported ACLs
The switch supports three applications of ACLs to filter traffic:
•
Port ACLs access-control traffic entering a Layer 2 interface. The switch does not support port ACLs
in the outbound direction. You can apply only one IP access list and one MAC access list to a Layer
2 interface.
Note
Port ACLs are not supported on ports configured with service instances.
•
Router ACLs access-control routed traffic between VLANs and are applied to Layer 3 interfaces in
a specific direction (inbound or outbound). The switch must be running the metro IP access image
to support router ACLs.
•
VLAN ACLs or VLAN maps access-control all packets (forwarded and routed). You can use VLAN
maps to filter traffic between devices in the same VLAN. VLAN maps are configured to provide
access control based on Layer 3 addresses for IPv4. Unsupported protocols are access-controlled
through MAC addresses using Ethernet ACEs. After a VLAN map is applied to a VLAN, all packets
entering the VLAN are checked against the VLAN map. Packets can either enter the VLAN through
a switch port or through a routed port after being routed.
You can use input port ACLs, router ACLs, and VLAN maps on the same switch. However, a port ACL
takes precedence over a router ACL or VLAN map.
•
When both an input port ACL and a VLAN map are applied, incoming packets received on ports
with a port ACL applied are filtered by the port ACL. Other packets are filtered by the VLAN map
